Epitaxial chemical vapor deposition is a process for growing a thin layer of material on a semiconductor wafer so that the lattice structure is identical to that of the wafer. Using this process, a layer having different conductivity type, dopant species, or dopant concentration may be applied to the semiconductor wafer to achieve the necessary electrical properties.
Prior to epitaxial deposition, the semiconductor wafer is typically mounted on a susceptor in a deposition chamber of a reactor. The epitaxial deposition process begins by introducing a cleaning gas, to a front surface of the wafer to pre-heat and clean the front surface of the wafer. The cleaning gas removes native oxide from the front surface, permitting the epitaxial silicon layer to grow continuously and evenly on the surface during a subsequent step of the deposition process. The epitaxial deposition process continues by introducing a vaporous silicon source gas to the front surface of the wafer to deposit and grow an epitaxial layer of silicon on the front surface. A back surface opposite the front surface of the susceptor may be simultaneously subjected to hydrogen gas. The susceptor, which supports the semiconductor wafer in the deposition chamber during the epitaxial deposition, is rotated during the process to ensure the epitaxial layer grows evenly.
A common susceptor design includes a disk having a recess with a concave or sloped ledge. Such a shape provides a benefit in that the wafer only contacts the susceptor very near the edge of the back surface, so damage to the polished back surface is reduced. With increasing angle of slope of the ledge, the damage to the polished back surface may be further reduced. However, wafers typically have an orientation feature, generally a notch, which may allow the silicon source gas flowing across the front surface of the wafer to leak between the wafer and the susceptor at the notch. The leaking source gas leads to excessive growth on the back surface of the wafer near the notch, which in turn degrades the flatness of the wafer.
Accordingly, a need exists for a susceptor that reduces or eliminates wafer back surface defects caused by leaking source gas and also for a susceptor that corrects deviations in the deposition rate of silicon source gas near the edge of the silicon wafer.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.